1. Field of the Invention
This invention relates generally to an apparatus for converting electrical signals into physical motion through the use of an electromagnetic transducer. In particular, the present invention provides a robust, low profile shaker system having an increased off center load acceptance which may be easily placed under an object in order to impart vibrational motion in response to electrical signals from a signal source.
2. Description of Related Art
The field of electrodynamic transducers for imparting shaking or vibrational motion is well established. The applicant for the present invention considered several prior shaker systems and noted the deficiencies listed below.
Existing electrodynamic shakers are designed to produce a cyclical force on a test subject or platform (typically using a load leveling suspension system) that is independently stable and sufficiently stiff in all directions except the intended direction of motion. The system shown and described in “Understanding The Physics of Electrodynamic Shaker Performance” (Sound and Vibration, October 2001 pgs 2–10) by George Fox Lang and Dave Snyder is one such system. Particularly, the moving portion of a voice coil actuated shaker can be damaged by loads in directions other than the direction of intended motion.
U.S. Pat. No. 6,389,900 shows a shaker design wherein the shaker is isolated from all forces on the test subject that are not aligned with the direction of intended motion or offset from the center of the coil. This is typically accomplished by coupling the two sides with a long thin rod called a stinger. The resulting assembly is complex, large and expensive.
Some shakers use a more integrated approach in which two plate style flexures are used to add stiffness in the transverse direction (perpendicular to the direction of intended motion) and support forces which are aligned with the intended direction of motion but offset from the coil center (moments). Examples of such systems can be found in the article “Electrodynamic Shaker Fundamentals” by George Fox Lang (Sound and Vibration, April 1997 pgs 1–8) and in the Labworks Inc “Shaker Engineering Info.” The two plates must be separated by a large distance to provide adequate moment stiffness. This adds complexity, limits armature displacement and greatly adds to the height of the system.
Still other shakers use a combination of a plate style flexure (which has little moment stiffness alone) above the actuator and a linear bearing on the opposite side, such as the shaker shown in Labworks ET-132-2 product description. The flexure and linear bearing must be separated by a large distance along the intended direction of motion to support large moments. This system however also has limited armature displacement, and adds to the overall height of the assembly.
Shakers also typically use flexible conductors to transmit energy from the actuator body or housing to the moving armature. These flexible conductors are prone to failure due to fatigue.
Thus, prior art shakers using a plate or leaf style armature spring to provide large transverse stiffness with a soft suspension stiffness (i.e. stiffness in the direction of intended armature motion) suffer by not achieving a large maximum load to suspension stiffness ratio (the smaller the suspension stiffness the larger the shaker efficiency) while maintaining a small shaker volume and support large moments. There is therefore a need for providing a robust and efficient shaker which can be flexibly, easily, and inconspicuously installed.